The present invention relates to a metal cored board and a method for manufacturing the same, which is used suitably for preparing a hybrid integrated circuit.
Up to this day, it has been proposed a method for preparing a plate board of hybrid integrated circuit having such a construction that an organic polymer film is adhered on its one surface with a foil of an electrically conductive metal for forming electric circits and also adhered on its another surface with an aluminium heat sink. The plate board, however, is poor in electrical breakdown strength, because most of the organic polymer films made by extrusion or casting have pinhols.
According to the studies of the present inventors, a plate board of hybrid integrated circuit having an excellent dielectric breakdown strength can be obtained by an insulating layer composed of a baked organic polymer instead of the above organic polymer film. The plate board is prepared by coating an electrically insulating varnish on the surface of an aluminium heat sink, baking the coated layer to form an electrical insulating layer, and then by adhering thereon a foil of an electrical conductive metal. The varnish can be applied, for example, by electrophoretical coating.
It is, however, difficult to form a baked layer tightly bonded on the surface of aluminium. On the other hand, it has been well-known in the technical field of electrophoretical coating of aluminium that the surface of the aluminium is treated with a zincate in advance of coating, in order to improve the bonding strength of the baked layer.
The present inventors found furthermore the fact that, though the bonding strength of a baked organic polymer layer on the surface of aluminium is improved by zincate treatment, it is not yet sufficient in the standpoint of being used in a plate board of hybrid integrated circuit. Namely, when such a plate board is heated locally in order to solder the aluminium heat sink or the electrically conductive metal layer to another electrical part, the baked organic polymer layer is peeled off from the aluminium heat sink.